Four patients with HIBM will be admitted to this study at the NIH Clinical Center for evaluation and IG treatment. The evaluation lasts about 1 month. After completing baseline studies (see below), patients receive two intravenous doses of immune globulin (on days 6 and 7), followed by measurement of muscle strength 2 days later (day 9). They receive additional IG infusions on days 13, 20, and 27. A final set of tests is performed on day 29. Patients may leave the hospital on pass when no studies are being done.